High-temperature heat-treating furnace



Feb. 20, 1945. w. WORTH E-rAL 2,369,879

HIGH TEMPERATURE HEAT TREATINa-FURNAGE Filed June 6, 1942 2 Sheets-Sheet 1 INVENTOR 5 we cozz M MATTORNEY Feb. 2o, 1945. f Q. WORTH TAL 4 2,369,879

HIGH TEMPERATURE HEAT TREATING FURNACE Filed June 6, 1942 2 Sheets-Sheet 2 :SYM/WTTORNEY Patented Feb.`2o,'1945 l l ICE accosta mon-TEMPERATUE HEAT-mamme FURNACE Weldon Worth, Day-ton, Ohio, and Edmund R. Walker, Kenmore, and Sidney A. Whitt, Buffalo, N. Y., assignors to. Feddrs ManufacturingCompany, Inc., Buffalo, N. Y.,ga, corporation ofr Newv York l. A"Application June 6, 1942, SerialfNo.l 446,064

` 7.1 claims.. tel. 26a- 15.)

This inventionA relates toa. furnace for heat Atreating various articlesl by means of a blast'of hot air or other gaseaand itis concerned partic- With a .circulating stream of air at relatively high, temperatures. i i j There are various articles, such as heat interchanger cores which are made of thin metallic tubes .and plates, which canr be integratedinto their final yform by the application of heat, nrovided, however, that the heatso applied is sufficient to 'effect the desired fusion without meltmg or warping or. otherwise spoiling .the work.r Of the various types orf furnaces heretofore, available, and to which the art has turned for this and other delicate operations, two may bomentioned.` In one, the Work is placed on the hearth and. isk heated, usually by radiant heat, in a stagnant atmosphere. natural lconvection being relied. upon Ato lbring the articles up to temperature.; In such a furnace, the upper temperature. lmnt depends, of course, primarily on the quantity of, heat supplied, by the heating elements and .heating-up portion of the cycle, and thus permits saturation of the inner portions before surfaceoverheating occurs. This type may be embodied insuceessful forms for low temperature applications, but has not heretofore `been applicable to high temperaturework.

One reasonfor such failure is due to the destructive effect ofwblasts of high temperature,v

atmospheresA on most materials ofcohstruction. Thus,v a-hot air or hydrogen blastl at a temperature much above 1500 Fahr. will corrode or embrittle steel or thecommon alloys of which fans `and blowers are made, v'vith` the result that the equipment soon. fails. vThe quest for more resistantmetals as' materials of construction has not .been successful. Accordingly, the COIIimOIl practicetoday is to turn over` articles requiring high temperature treatment to skilled workmen vfor hand. processing during the course of assembly-a method which adds tremendously to manufacturing 'costs and curtails the output of vitally needed equipment.. f

Thev present invention providesia solution for lthese problems Aby means which` effect the propulsionfand circulation of. the air as. though the furnace were operating in a sai-e lowternf peraturerange, together with means forsupplyularl'y with` the provisionofmeans yfor `heating ing heatv to the moving atmosphere to bring its, temperature intofthe high` temperature range. The furnace accordingly operates without the destructivo eect just noted, and also takesadvantage of the benets oi.y a forced draft type,

thereby permitting delicate Worl; to be heat will be appreciated byl those skilled in the art,`

moreover provides a toolor instrumentality for the extension of, hydrogenbrazing to applications not previously deemed feasible.,

-Qne form or embodiment of the principles 0f the invention is illustrated in the accompanying drawings, wherein: n y

Fig. 1 is a, vertical section through a typical installation, showing the components thereof; and

Eig. 2 is an end view. Apartially in section and partially in elevation, taken substantially along the line 2..-2 .of Fis. 1-

Referring first to Fig. 1, the numeral I0 designatos a heat treating ,furnace including a hearth or Work-receiving platform Il upon which may be plaoed ione or more articles `l2 to be heat treated. The .platform l! preferably is perforated at least :at its end portions I3 and I4 for the admission andwithdrawal ofI a hot gas blast, and it may be p-rovidedon its underside with one or more adjustable bafes I5 so thatl a portion of the entrant air may be diverted through portions-'of theL Work-,a provision enabling more rapid saturation olf Such articles as heat exchange cores wherein dual flow through and around the tubesmay be effected. Access to the platform Il is,r had through a door I1 yconveniently located with respect to the-,floor or handling platform I8; Sothat the work I2 can be inserted and removed as desired.

The furnace I0 and its ,contents are heated by means of 'a forced `draft of gassuch as air, hydrogen, or nitrogen, which enters through a flue- 2| for flow through the platform AIl and around the work, and whichv is removed through a flue 22. vAs thus far described, the furnace corresponds generally vto ,known types of anllaratus, and therefore a more extended discusof the materials of construction and fabrication is believedto he superfluous. It may simply be vnoted herefthat. as will appear from the following portions of the description, it isintended that the entering gas may he at e. Vrelatively high temperature, say 2000.n to 24,400? Fahr., which is appreoiably above the temperatures heretofore tolerated,'and therefore the brickwork and 1inhg shouldhe chosen to withstand such-temperatures for a long time. The platform Il vand baiiles i5, being simple bar and plate forms, mat7 be permitted-Lto suffer deterioration, since they are cheap and are designed for ready replacement. Under such entrance conditions, and

depending upon the velocity of the draft and the heat absorbing nature of the work I2, the returning atmosphere may be at any temperature from say 100 to 400 degrees lower than the entrance temperature.

Upon inspection of Fig. l, it will be seen that air leaving the furnace l through the flue 22 'travels in a figure eight path en route to the entrance ue 2i. In successive order from the flue 22, the returning atmosphere passes through one pass of a heat interchanger 25, flows thence to a cooler 26, is then inducted into a blower 21 for discharge through the other pass of the interchanger 25, is heated by the heater 28, and is then admitted into the entrance 2l for recirculation through the furnace I0. This cycle therefore contemplates successive temperature reductions in the return gas in the heater interchanger and the cooler, whereby the blower handles relatively cold gas, and successive heatings of the forced draft in the interchanger and heater. The blower accordingly operates at permissible low temperatures, while the furnace operates at high temperatures on the forced draft, closed cycle principle, a result which, as it is believed, has not heretofore been attained The heat interchanger 25, which is connected to the flue 22 by the elbow 3|, consists of a con-v ventional form of spaced tube core, and is so installed that the returns flow in the spaces around the tubes. The returns thus correspond to the hot gases in a Water tube type of boiler, the blower discharge passing through the tubes 32. A certain amount of the sensible heat of the returns is accordingly extracted with the result that the temperature will drop (depending, always, 0f course, on particular operating conditions) to say 1800 Fahr. from 20002100. The partially cooled returns then flow through the elbow 33 into a downcomer 34, and thence, through a lateral elbow 35 (see Fig. 2) through the tubes 36 of the cooler 2B. Here, it will be noted, the flow of the returns through the cooler 2B is in fire tube fashion.

The cooler 2B is herein illustrated as a forced draft air cooled type, although it will be understood that water cooled types may be used if provision is made to take care of the steam volumes which tend to form at the temperatures just indicated. The cooler 26 is connected by a duct 31 to the discharge side of an auxiliary blower 38, operated by a motor or other source of power, not shown, and which serves to force a blast of cold air around the tubes 3B. The opposite face of the cooler 26 is connected to a waste duct 39, by means of which the heated air may be sent to waste, or conveyed to a combustion type boiler or other equipment where the heat of the air blast may be used to advantage. In the present embodiment of the invention, it` may be assumed that the cooler 26 is of such size as to reduce the atmosphere from the furnace l0 to about l400 Fahr., which is a safe temperature for the blower and other parts of the installation. Obviously, greater cooling may be effected if operating conditions so warrant.

Upon emerging from the cooler 26, the returns enter a U bend 42 which connects to a duct 43 terminating in the suction chambers 45 of the blower 21. This unit is of the squirrel cage type, having a rotor 46 mounted on a shaft 41 which is belt-driven by the motor 48. The snail 43, or discharge side of the blower, is connected to a riser 5l which is lined up with the entrance flue 2|, as best shown in Fig. 1.

As previously noted, the blower discharge flows through the tubes 32 of the heat lnterchanger 25,

wherein it was assumed, for examples sake, that the hot returns had been reduced in temperature some two or three hundred degrees. The heat lost by the returns is taken up by the blower discharge, so that the gases entering the riser 5l, and which were considered to be at about 1400", are now reheated to say 1700. This, however, is below the desired entrance temperature for the furnace I 0.

Accordingly, an electric resistance heater 28 is positioned in advance of the platform Il. The gases leaving the interchanger 25 at the region marked 52 flow around a number of heating elements 53 supported on end plates 54, and which are accessible through a removable panel section 55 of the flue wall. These elements are advantageously made of a highly resistant material such as silicon carbide, which will withstand temperatures in excess of 2400", and to which the electric current is supplied by means of bus' bars 56. Obviously, the selection of the materials here will depend upon the desired temperature for the furnace atmosphere, and under some conditions it may be found preferable to'use flame heat. Temperature regulation may be obtained by the usual forms of thermostatic control. In any event, the re-heated furnace atmosphere now enters the furnace Hl through the flue 2|, thus completing the cycle.

It will thus be seen that, while in the common form of hot blast furnace, it is the custom to supe plymake-up heat to the circulating gases equal to the amount of heat lost to the work, the present invention contemplates the wilful extraction of much greater quantities of heat from the returns, although, of course, such extracted amounts must later be replenished. This, of course, appears to be a futile waste of energy, since whatever is lost to the cooler 26 must be compensated by additions from the reheater 23. This effect does exist, but it is reduced to a minimum by providing the heat exchanger 25 which restores to the circulating gases some of the energy taken from the returns.

As hereinabove pointed out, however, this energy loss, or rather, the cost of extracting and replenishing the heat, becomes an economical price topay for the results which may be obtained in heat treating. There are many applications for the hydrogen brazing or welding method if the time cycle could be curtailed by using forced draft, and such applications are now made possible. Again, the `destructive effect of high temperature gases has precluded successful use of forced draft, which may now be applied. The case of the thin walled heat interchanger initially noted is but one such application. It is believed unnecessary to multiply the examples, since those skilled in the art can utilize the present invention for various conditions and processes.

It is also to be understood that while certain simple forms of heat interchangers and coolers have been described, no novelty is claimed for them in detail, and the particular forms discussed have been chosen because of their simplicity and the facility with which they lend themselves to rapid installation. Each of the various elements of the system may obviously be substituted by such other formas the user may deem preferable. Likewise, the temperatures set forth herein are merely for exemplary purposes, and will naturally vary with conditions. It is therefore intended that the foregoing description shall be posed thereon except considered as illustrative ofthe princziplesiofy the invention, and that `no limitationsshallbeA imas'are set forth in the following claims. y n We claim: f l

v1. In a `heat treating furnace having a plat-v form for the work to be treate-d, an entrance ue l for the admission of hot gas to the work, and a return nue forvthe withdrawal of the gas, a blower` having-an inlet connected to the return flue and an outlet connected to the entrance flue, means inthe return iiue inadvance of lthe blower'for cooling the return gases to a temperature at which they cause no material deterioration of the material ofy the blower, means in the entrance.

flue on the discharge side of the blower for heating the admitted gases to a selected temperature which would cause deteriorationy of the material' the returning gas a portion of the heat thereinl a cooling member connected to said one pass to receive return gas from said interchanger for further removing heat; from the return gas, said cooling member being positioned in advance of the inlet of the blower, said blower outlet being connected tothe other pass of the' heat interl changer, and a heating member interposed in the entrance flue between said last named pass and said furnace member.y f I 5. A method `of heating objects uniformly to a selected temperature which comprises placing 1 an object to beheated in a closed chamber, circulating the same body of a gas as a confined, closed stream through said chamber in a con- Y tinuous, closed circuit, crossing the portionsI of of the blower, said cooling means and said heat- 'blower having an inlet connected to thereturn flue and an outlet connected to the entrance flue, heating means interposed in the entrance flue between the outlet of the blowerv and thefurnace member` for supplyingy heat 'to the gas, a. heatv interchanger with separate passages having onel of the passagesl also interposed in: series in the entrance flue between the outlet of the blower and the saidheating means, said return flue also being connected through the other of said passages of said heat interchanger' at a zone between said furnace member and the inlet of the blower.

3. A forced draft heattreating furnace comprising a furnace member having a work receivingk platform, an entrance flue vconnected-to the furnace member to supply hot gas to the work,

` a return flue connected to the furnace member forvwithdrawing the gas, said flues and member forming a closed, endless conduit in which the gas is circulated repeatedly, a blower for recirculating the gas from the return ue to the-en- 'trance flue, cooling-means interposed in thereturn ue between the furnace member and the blower, said cooling means comprising a heat interchanger and a separate cooler, heating means interposed in the entrance 1l-ue between the blow# er and said furnace member, said heating means comprising theaforesaid heat interchanger and a further heating member;

n 4. A forced draft heat treating furnace comprising a furnace member having a workreceiv- Ling platform. spaced lentrance and return flues i crossing portions in a direction of movement of said stream, whereby thefcooling of the stream said stream moving towards said chamber with the portion leaving saidv chamber, in heat exchanging relation to each other, heating the "gas entering said chamber in a zone between said crossing stream portions and said chamber, cooling the gas leaving said chamber in a Zone after it passes said heat exchanging relation and before it returns to said heat exchanging relation,

and applying a circulating force to-said gas stream between said cooling zone and the heat exchanging relation.

. 6. In the heating of an object uniformly and rapidly by a circulating stream of gas in which it is placed, to a temperature which would be destructive to a blower used tocirculate said gas as a stream, the improved method of forcibly circulating the gas as a confined stream in a closed major loop path in which path has spaced apart portions crossing in separate stream portions to form two minorloops, placing the object to beheated'in'the stream in one of said minorfloops, effecting a heat exchange between l the gas of the stream in the crossing portions thereof, heating the'gas of said stream 'in said one loop between the crossing portions .and said object in a Azone in whichthe stream is moving from the crossing portion tosaid object, cooling. the gas of said stream in a zone of the other of l. said minor loops, and applying the circulating force to said stream ina zone of said other minor loop between said cooling zone and the immediately before the circulating force is applied thereto will protect any mechanismy in the stream used to apply that force, and the heat losses will be a. minimum.

7. In the heating of an object uniformly and rapidly, by placing it in a heated stream of gas circulated in a closed path by a mechanicalblower, toa critical temperature which would be un duly destructive upon said blower, that improve` ment therein whichv comprises the steps of cooling the gas of the stream passing the object before it reaches the blower, effecting a heat exchange between the gas of the stream in the porconnected to the 'furnace member for admitting hotgas to and withdrawing 4spent gas from the platform, said flues and member together-,forming a closed, endlessconduit through which the gas is circulated repeatedly, a blower'having an inlet connected to the return flue and an outlet j connected to the entrance, flue, a heat interchanger with 'separate passes and having one.

pass interposed in the return flue to absorb` from tion leaving the blower and beforev it reaches said object, andV the portion of the stream 4leaving saidobject and-before it is cooled, yand heating .the portion of the stream lapproaching the object from the blower after its heat interchange with the portion of the stream leaving the object.

wELDoN WORTH. EDMUND R. WALKER. SIDNEY A. WHIT'r. 

